1. Field of the Invention
The present invention relates to a novel process for producing a fat and oil composition for deep-frying. The present invention particularly relates to a process for producing a fat and oil composition for deep-frying by which the fat and oil is suppressed in deterioration during heating and cooking, in particular color development and unfavorable odor during heating, and deep fried food or the like has an improved crisp.
2. Description of the Related Art
As oil for cooking deep fried food such as fried foods or Tempura (Japanese dish made of battered and deeply fried seafood or vegetables), liquid oils such as soybean oil and rapeseed oil are used. These kinds of liquid oils are low-cost and can be handled favorably but cause color development, increased viscosity, unfavorable cooked odor or the like during heating and cooking. Promotion of the deterioration of liquid oil causes the worsening of the quality of the deep fried food, thus preventing the liquid oil from being used for a long time.
As a related art for suppressing the color development by heating during deep-frying by using liquid oil, a method has been used to enhance the refining conditions in order to minimize phospholipid, Fe component or the like known as a substance that promotes the deterioration of fat and oil during heating. However, the current refining conditions of liquid oil are significantly enhanced already. Thus, enhancing the refining conditions any more may worsen the fat and oil on the contrary.
In order to improve the heat stability of fat and oil, a technique for blending emulsifier or the like, a transesterification technique, and a technique for subjecting oil bearing seeds to hybridization, mutation, gene recombination or the like have been suggested to provide an arbitrary fatty acid composition. However, such techniques require a high cost and may require a new obligation to indicate an additive or the like.
As a method for allowing a certain amount of phosphorus-derived components in fat and oil, Japanese Unexamined Patent Application Publication No. 2006-121990 (Patent Document 1) suggests a method for refining crude oil by degassing and dehydration process under reduced pressure without subjecting the crude oil to a degumming process. On the other hand, Japanese Unexamined Patent Application Publication No. S58-194994 (Patent Document 2) suggests a method for subjecting crude oil to an ultrafiltration membrane instead of a conventional degumming process to remove impurities such as phospholipid without using an agent or the like. Japanese Unexamined Patent Application Publication No. H9-157687 (Patent Document 3) suggests a method for directly subjecting degummed or neutralized oil of soybean oil, rapeseed oil or corn oil to deodrization process to obtain a fat and oil composition having a radical scavenging activity and having a low degree of refining. These methods are tried for a totally different objective.
According to the method of Patent Publication 1, phospholipid as a phosphorus-derived component can be caused to remain in a large amount. However, this method is for a fat and oil processed food. Since it is generally clear that a very high amount of phospholipid of a few percent causes a significant color development (brownish discoloration) of the fat and oil during heating and cooking, this method cannot be used for an application for deep-frying or the like. Regarding the relation between the phosphorous component and the phospholipid content, oil bearing seeds generally include phospholipid of a molecular weight of about 750 to 800. Since phosphorus has an atomic weight of 31, an about 25 times-larger-amount of phosphorus content corresponds to phospholipid.
In the case of the method of Patent Document 2, phospholipid as a phosphorus-derived component remains in a certain amount. However, this method requires a high cost and thus is not suitable for mass production with a low cost. Furthermore, the functionality in the cooking with heat does not show, as shown in the Example, a particular improvement in the quality compared to the conventional product. In the case of the method of Patent Document 3, a bleaching process for refining fat and oil is omitted and thus phosphorus-derived components remain in a large amount. However, components known as promoting photooxidation (e.g., chlorophyll) also tend to remain, thus causing a risk of an adverse effect on the preservative quality of the fat and oil and the fat and oil foods. As described above, the methods according to the conventional techniques cannot suppress the color development by heating of a fat and oil composition for deep-frying.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-121990    Patent Document 2: Japanese Unexamined Patent Application Publication No. S58-194994    Patent Document 3: Japanese Unexamined Patent Application Publication No. H9-157687